1. Field of the Invention
The present invention relates to a step zoom lens camera in which a focusing operation is carried out by controlling the angular displacement of a cam ring having a cam groove.
2. Description of the Related Art
In classical zoom lenses, upon zooming, a plurality of variable power lens groups are moved along predetermined zooming path, so that the focal length can be varied without moving the focal position. In a shutter release operation, a focusing lens group is moved in accordance with the object distance. The focusing lens group is either provided separately from the variable power lens groups or is formed by one of the variable power lens groups. Classical zoom lenses of this kind have been used for a mechanical zoom lens in which a cam ring having cam grooves is manually or electrically rotated in a stepless fashion.
A step zoom lens has been used for a lens in which the angular displacement of the cam ring with cam grooves is pulse-controlled. In such a step zoom lens, the focal length from the telephoto extremity to the wide angle extremity is divided into a plurality of (finite number of) focal length steps. The angular displacement of the cam ring is controlled at each focal length step so as to focus on an object of any distance between the infinite object distance and the closest (minimum) object distance, during the focusing operation while the zooming operation is carried out. The angular distance of the cam ring is pulse-controlled so that the object is in-focus in accordance with the focal length belonging to a specific focal length step determined in accordance with object distance data.
In the step zoom lens, if an area of the cam ring outside of the effective area (step area) of the cam grooves is used upon focusing, due to a deviation of the attachment angle of the cam ring, an out-of-focus (defocus) state occurs. Such defocusing in a zoom lens is caused by other various reasons. In particular, in a step zoom lens, it is preferable that whether or not the cam groove area is correctly used at each focal length step (i.e., whether or not the angular position of the cam ring is appropriate) be easily checked. In some types of step zoom lenses, the step area of the cam grooves includes an adjustment area for focus adjustment in addition to a cam groove area for focusing over the object distance from the infinite object distance to the closest object distance. Accordingly, it is preferable to be able to easily identify the area of the step area, which includes the adjustment area, which is actually being used.
It is an object of the present invention to provide a step zoom lens camera in which the state of use of the cam groove at each focal length step or the angular displacement of the cam ring can be easily confirmed.
In order to achieve the above mentioned object, a step zoom lens camera is provided including a rotatable cam ring; a cam groove formed on the cam ring, the cam groove including a plurality of step areas, formed by splitting a focal length from the wide angle extremity to the telephoto extremity, and transit areas which connect the plurality of step areas to form a step zoom path; a linear movement member which is connected to the cam ring so as to rotate relative thereto and to move together in the optical axis direction; and a cam-guided lens group which is guided by the linear movement member to move linearly in the optical axis direction in accordance with the cam groove so as to move to an in-focus position of an object, from an infinite object distance to a closest object distance, within a step area of the cam groove. The cam ring is provided on the rear end surface thereof with a plurality of step area indicating indexes which are spaced from one another in the circumferential direction to represent the corresponding step areas. The linear movement member is provided with a reference index at a predetermined circumferential position thereof, so that the position of use of the cam groove can be visually confirmed by viewing the position of the step area indicating indexes relative to the reference index.
In an embodiment, the step zoom lens camera further includes a focusing lens group which serves as a variable power lens group, in addition to the cam-guided lens group which is guided by the cam groove, the focusing lens group being moved in the optical axis direction in a linear relationship to the angular displacement of the cam ring when the cam ring is rotated.
In an embodiment, the linear movement member includes an annular portion which covers the rear end surface of the cam ring, wherein the reference index includes a window which extends through the annular portion and which is elongated in the circumferential direction. The cam-guided lens group is guided in each step area of the cam groove when each step area indicating index is located in the window.
Preferably, each of the step area indicating indexes is a recess formed on the rear end surface of the cam ring.
Preferably, the cam groove is provided with an accommodation area which is adapted to hold the cam-guided lens group in an accommodation position at which no photographic exposure is carried out. The cam ring is provided on the rear end surface thereof with an accommodation area indicating index which represents the position of the accommodation area in the circumferential direction.
Preferably, each step area of the cam groove includes a focusing area in which the cam-guided lens group is moved to a focal position in which an object from an infinite distance to the closest distance can be focused on, in accordance with the rotation of the cam ring; and adjustment areas which are provided on opposite sides of the focusing area and which are adapted to move the cam-guided lens group in the optical axis direction while maintaining a focusing function, when the angular position of the cam ring is changed.
In an embodiment, the step areas of the cam groove have different lengths, and a length of the window in the circumferential direction corresponds to a longest step area of the step areas. Each the step area indicating indexes is positioned at one and the other ends of the window when the cam-guided lens group is guided at a corresponding one and the other ends of each corresponding the step area.
In an embodiment, the step area indicating indexes have different lengths in the circumferential direction.
According to another aspect of the present invention, a step zoom lens camera is provided, in which the focal length from the telephoto extremity to the wide angle extremity is split into a finite number of focal length steps, so that a zoom lens system can be moved to a focal position in which an object from a infinite distance to the closest distance can be focused on, by controlling the angular displacement of a cam ring with a cam groove at each focal length step to vary the focal length. The cam ring is provided on the rear end surface thereof with a plurality of step indicating indexes which are spaced from one another in the circumferential direction to represent the angular position of the cam ring corresponding to the focal length steps. A linear movement member is provided with a reference index at a predetermined circumferential position thereof, the linear movement member is connected to the cam ring so as to rotate relative thereto and to move together in the optical axis direction. The angular position of the cam groove at each focal length step can be visually confirmed by viewing the relative position of the step indicating indexes relative to the reference index.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 2000-264110 (filed on Aug. 31, 2000) which is expressly incorporated herein by reference in its entirety.